Ionospheric convection response to slow, strong variations in a northward interplanetary magnetic field: A case study for January 14, 1988

first_imgWe analyze ionospheric convection patterns over the polar regions during the passage of an interplanetary magnetic cloud on January 14, 1988, when the interplanetary magnetic field (IMF) rotated slowly in direction and had a large amplitude. Using the assimilative mapping of ionospheric electrodynamics (AMIE) procedure, we combine simultaneous observations of ionospheric drifts and magnetic perturbations from many different instruments into consistent patterns of high-latitude electrodynamics, focusing on the period of northward IMF. By combining satellite data with ground-based observations, we have generated one of the most comprehensive data sets yet assembled and used it to produce convection maps for both hemispheres. We present evidence that a lobe convection cell was embedded within normal merging convection during a period when the IMF By and Bz components were large and positive. As the IMF became predominantly northward, a strong reversed convection pattern (afternoon-to-morning potential drop of around 100 kV) appeared in the southern (summer) polar cap, while convection in the northern (winter) hemisphere became weak and disordered with a dawn-to-dusk potential drop of the order of 30 kV. These patterns persisted for about 3 hours, until the IMF rotated significantly toward the west. We interpret this behavior in terms of a recently proposed merging model for northward IMF under solstice conditions, for which lobe field lines from the hemisphere tilted toward the Sun (summer hemisphere) drape over the dayside magnetosphere, producing reverse convection in the summer hemisphere and impeding direct contact between the solar wind and field lines connected to the winter polar cap. The positive IMF Bx component present at this time could have contributed to the observed hemispheric asymmetry. Reverse convection in the summer hemisphere broke down rapidly after the ratio |By/Bz| exceeded unity, while convection in the winter hemisphere strengthened. A dominant dawn-to-dusk potential drop was established in both hemispheres when the magnitude of By exceeded that of Bz, with potential drops of the order of 100 kV, even while Bz remained northward. The later transition to southward Bz produced a gradual intensification of the convection, but a greater qualitative change occurred at the transition through |By/Bz| = 1 than at the transition through Bz = 0. The various convection patterns we derive under northward IMF conditions illustrate all possibilities previously discussed in the literature: nearly single-cell and multicell, distorted and symmetric, ordered and unordered, and sunward and antisunward.last_img read more

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Manchester United to leave City in pole position for Pep Guardiola

first_imgManchester United intend to take a back seat when Pep Guardiola’s contract with Bayern Munich expires at the end of the season, leaving the way open for Manchester City to pursue the former Barcelona coach at the expense of Manuel Pellegrini.United’s information is that Guardiola will not renew his current deal and wants to work in English football but that will not interest them because of the timing of his availability and their support for Louis van Gaal.The suspicion at Old Trafford is that Guardiola’s most likely destination will be City, meaning an obvious threat to Pellegrini’s job, although Chelsea could be another viable alternative given their decline this season under José Mourinho.Ordinarily, United would have Guardiola prominently in their thoughts bearing in mind his success at Bayern and previously at Barcelona, where his team twice beat Sir Alex Ferguson’s sides in Champions League finals. However, if he were to leave Bayern next summer that would count against United, given it comes a year before Van Gaal’s contract expires.The Dutchman’s deal runs until 2017 and unless something drastically changes United will take themselves out of the equation if Guardiola is available.Pellegrini’s position at City is not so watertight and not helped by the fact Saturday’s 2-0 defeat at Stoke was the third time they have been beaten in the last five matches. Pellegrini signed a contract extension in August to take him to the end of the 2016-17 season but Guardiola’s availability has been in the minds of the chief executive, Ferran Soriano, and the director of football, Txiki Begiristain, for some time. They worked with Guardiola in their previous roles as executives at Barcelona and consider him an ideal fit for a club that had expected more than Pellegrini has been able to deliver.Pellegrini’s team have not won an away match in the Premier League since September and he admitted they had played badly against Stoke, giving Leicester City the chance to return to the top of the division courtesy of a 3-0 win at Swansea City.Riyad Mahrez scored a hat-trick as Claudio Ranieri’s team established a two-point lead ahead of Arsenal, 3-1 winners at home to Sunderland, on a day when Jamie Vardy’s 11-match scoring run came to an end. “We didn’t play well,” Joe Hart, Manchester City’s goalkeeper, said after two early goals from Marko Arnautovic won the game. Pellegrini blamed fatigue but Hart chose not to follow the same line. “A few of the lads are feeling it from the games we are playing but that is not an excuse. We need to put in at least a seven-out-of-10 performance every game and we are not doing that. We can’t accept how we played.” United dropped to fourth position after their latest 0-0 draw, at home to West Ham United, and have now scored seven times in the last 10 matches. It was their fifth goalless draw in the last nine matches but, despite growing scrutiny of the team’s style, there is strong support for Van Gaal behind the scenes at Old Trafford. The boardroom view is that the criticism has been overplayed and that it is satisfactory for now that Van Gaal has re-established the club as credible title challengers.Ed Woodward, United’s chief executive, is still hopeful that United will eventually be able to lure one of Cristiano Ronaldo, Neymar or Gareth Bale. However, he is not hugely optimistic about adding any more players in the January transfer window, mindful of the way Southampton blocked their attempts to sign Sadio Mané in the summer. United need cover at left-back but the idea of offering Ashley Cole a short-term deal has been discounted.–Catch the EPL 2014/15 games live on SuperSport throughout the season.last_img read more

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